Opioid dependence (OD) is a common disorder in many regions worldwide that causes considerable social, medical and psychiatric disability. Current data demonstrate the importance of genetic factors in its etiology (Kendler, Jacobson, Prescott, & Neale, 2003; Tsuang et al., 1996), and there is a strong expectation of genetic heterogeneity and complex inheritance. Human research has identified several promising candidate risk loci contributing to OD in nonisolates (Gelernter et al., 2006). However, advances in methods for the genetic analysis of complex traits, including recent successes in identifying genes for common disorders in genetically and environmentally isolated populations has led to a global interest in the study of such specialized groups, which pose several theoretical advantages for gene mapping (Peltonen, Palotie, & Lange, 2000).
